Encyclopedia of Microtonal Music Theory

augmented-4th / aug4 / #4 / +4

[Joe Monzo]

A diatonic interval which is one chromatic semitone larger than the perfect-4th of the diatonic scale. The augmented-4th is composed of 3 tones (i.e., whole-tones).

The augmented 4th occurs naturally in every diatonic major and harmonic-minor scale, between the "subdominant" (4th degree or "IV") and the "leading-tone" (7th degree or "VII"). Example, in the key of C-major ("t" = tone, "s" = semitone) :